As a detector of a liquid chromatograph, an absorptiometric detector is known. The absorptiometric detector is provided with a flow cell having a flow path (cell) that allows a sample solution eluted from a separation column to pass through (see Patent Document 1). The absorptiometric detector quantifies a sample component concentration in a sample solution flowing through a cell by irradiating light of a predetermined wavelength region from a light source against a flow cell, measuring the intensity of the light transmitted through the flow cell with a light detector, and obtaining the absorbance at a given wavelength region.